WCAG 2: The difference between a level and a priority

Summary

The draft version of the Web Content Accessibility Guidelines (WCAG) uses success criteria that is organised into three levels of conformance. The method of grouping the success criteria differs in important ways from the approach taken in WCAG 1.0 where priorities are assigned to checkpoints, but I'm buggered if I understand the importance of the new approach. It seems to me that swapping the word "priority" with the word "level" is meant to imply that level 3 success criteria should be considered important, whereas priority 3 checkpoints shouldn't.

Author: Gez Lemon

Anyone familiar with WCAG 1.0 will also be familiar with the priority scheme that is used to determine the importance of each checkpoint in the guidelines:

Each checkpoint has a priority level assigned by the Working Group based on the checkpoint's impact on accessibility.

[Priority 1]

A Web content developer must satisfy this checkpoint. Otherwise, one or more groups will find it impossible to access information in the document. Satisfying this checkpoint is a basic requirement for some groups to be able to use Web documents.

[Priority 2]

A Web content developer should satisfy this checkpoint. Otherwise, one or more groups will find it difficult to access information in the document. Satisfying this checkpoint will remove significant barriers to accessing Web documents.

[Priority 3]

A Web content developer may address this checkpoint. Otherwise, one or more groups will find it somewhat difficult to access information in the document. Satisfying this checkpoint will improve access to Web documents.

Instead of using checkpoints, WCAG 2.0 draft uses success criteria that is organised into three levels of conformance:

Level 1 success criteria

Achieve a minimum level of accessibility through markup, scripting, or other technologies that interact with or enable access through user agents, including assistive technologies.

Can reasonably be applied to all Web resources.

Level 2 success criteria

Achieve an enhanced level of accessibility through one or both of the following:

markup, scripting, or other technologies that interact with or enable access through user agents, including assistive technologies

the design of the content and presentation

Can reasonably be applied to all Web resources.

Level 3 success criteria

Achieve additional accessibility enhancements for people with disabilities.

Are not applicable to all Web resources.

The following explanation is given for the method of grouping success criteria in WCAG 2.0:

This method of grouping success criteria differs in important ways from the approach taken in WCAG 1.0. In WCAG 1.0, each checkpoint is assigned a "priority" according to its impact on accessibility for users. Thus Priority 3 checkpoints appear to be less important than Priority 1 checkpoints. The Working Group now believes that all success criteria of WCAG 2.0 are essential for some people. Thus, the system of checkpoints and priorities used in WCAG 1.0 has been replaced by success criteria grouped under Levels 1, 2, and 3 as described above.

Recognising that all success criteria are essential for some people is admirable, but the new wording still ranks each success criterion according to its impact on accessibility for users. What is the difference between a minimum level of accessibility, and an enhanced level of accessibility? Once you've formulated an answer to that question, how does that differ from the priority system used in WCAG 1.0?

For any given level, all success criteria for that level, and the success criteria for all levels below, must be met before a conformance claim can be made. Therefore, each level is inferred a level of importance; otherwise, they would all be considered equally important, and ranked only as to whether or not they can reasonably be applied to all web resources.

What exactly does "supported" mean here? Does it mean that the user agent is conforming according to the conformance criterea of the respective technology? Because if that is the case WCAG 2.0 would be quite useless taken into account that most software does not have fully conforming implementations.

They don't mean that the user agent conforms to the conformance criteria of the respective technology, but that the user agent itself is accessible to people with disabilities. In a perfect world, they would require that the user agent conforms to the User Agent Accessibility Guidelines (UAAG), but there isn't a single user agent that conforms to UAAG, so they've opted for supported by accessible user agents. It still leaves a problem, as the meaning of accessible user agents is subjective.

I don't understand what your issue is. The priorities in WCAG 1.0 talks of the difficulties for user groups - the levels in WCAG 2.0 focuses on techniques to achieve accessibility. The WCAG 2.0 approach is much better imho.

I don't understand what your issue is. The priorities in WCAG 1.0 talks of the difficulties for user groups - the levels in WCAG 2.0 focuses on techniques to achieve accessibility. The WCAG 2.0 approach is much better imho.

My issue isn't so much with the wording of WCAG 2.0's success criteria system; it's more about how it "differs in important ways", with an explanation that suggests the former approach puts too much emphasis on the importance of a checkpoint, whereas a level isn't meant to imply any importance. I simply don't understand it. But as you've mentioned that WCAG 1.0 talks specifically about difficulties for user groups ...

Accessibility is entirely about ensuring that people are not discriminated against, and that everybody, regardless of whether or not they have any disabilities, has equal access to content. It's about people, so it's not wrong or even misguided to talk about the effect a barrier or an enhancement has on people.

The new success criteria is organised into levels, with wording and a numbering scheme that infers the importance for each level. Level 1 (minimum level of accessibility), level 2 (enhanced level of accessibility), level 3 (additional enhancements - not applicable to all web resources). If we're talking about a minimum level of accessibility, then we're talking about issues that authors must satisfy; otherwise, one or more groups will find it impossible to access the content. If we're talking about an enhanced level of accessibility, then we're talking about issues that authors should satisfy; otherwise, one or more groups will have difficulty accessing the content. The language used for WCAG 1.0 priorities applies to WCAG 2.0 levels, so I fail to see how it "differs in important ways".

In practical every day terms, there is no difference between the terms "priority 1" and "level 1" for me.

Over drinks we could debate the finer details, but in the real world, I'd tell people, if you don't bother to do all of "1" then you've locked the door to your content(and that isn't very nice.)

I'm not sayin' I'll be stoppin' at level 1, but I will help people prioritize based on the levels (just like I do with priorites now).

Last but not least, I'm pleased with the change of terms for a couple of reasons. First, if I hear you say "Level 1" (and you know what you are talking about) I instantly know you are talking about WCAG 2.0. Second, I love the addition of the phrase "Can reasonably be applied to all Web resources." I get so passionate about accessibility, that it is important to remind me to be reasonable!

It means that all success criteria is important but can be written so that it only applies at the appropriate level for a given technology. If a success criteria only applies to Flash then it can be stated at level 3. Simple!

It means that all success criteria is important but can be written so that it only applies at the appropriate level for a given technology. If a success criteria only applies to Flash then it can be stated at level 3. Simple!

If that were true, then I would obviously agree. A quick look through the different success criteria, and it's immediately apparent that that is not the case.

Consider Guideline 1.4: Make it easy to distinguish foreground information from background images or sounds. Success criterion 1.4.1 is a level 2 success criterion that requires that text or diagrams, and their background, must have a luminosity contrast ratio of at least 5:1. Success criterion 1.4.3 is a level 3 success criterion that requires that text or diagrams, and their background, must have a luminosity contrast ratio of at least 10:1.

What technology enables a contrast ratio of 10:1 that couldn't reasonably be applied to all web resources, whereas a contrast ratio of 5:1 is quite reasonable for all web resources? It's clearly been put at level 3 because whilst it requires a stronger contrast, it's more difficult to achieve. It has nothing whatsoever to do with technology, and everything to do with importance - 10:1 would be fantastic, but they'll settle for 5:1 as being suitable for most people.

And contrast isn't considered important enough to reach a minimum level of accessibility. On the surface, that might appear to be a reasonable assumption. If content and presentation are separate, the user can either use their own style sheet, or disable styles completely and revert to the browser's default style sheet. But that's technology dependent - how do you separate the foreground and background information from a bitmapped image? A requirement that it is easy to distinguish foreground information from the background can reasonably be applied to all technologies, and is essential to meet a minimum level of accessibility, but the levels given to the success criteria do not reflect that.